Several medical disorders appear to be related to partial or complete obstruction of an individual's pharyngeal airway during sleep. As described in the applicant's prior U.S. Pat. Nos. 5,365,945, 6,041,784 and 6,161,542, the disclosures of which are hereby incorporated by reference, snoring and obstructive sleep apnea are typically caused by complete or partial obstruction of an individual's pharyngeal airway resulting from the apposition of the rear portion of the tongue or soft palate with the posterior pharyngeal wall. Obstructive sleep apnea is a potentially lethal disorder in which breathing stops during sleep for 10 seconds or more, sometimes up to 300 times per night. Snoring occurs when the pharyngeal airway is partially obstructed, resulting in vibration of the oral tissues during respiration. These sleep disorders tend to become more severe as patients grow older, likely due to a progressive loss of muscle tone in the patient's throat and oral tissues.
Habitual snoring and sleep apnea have been associated with other potentially serious medical conditions, such as hypertension, ischemic heart disease and strokes. Accordingly, early diagnosis and treatment is recommended. One surgical approach, known as uvulopalatopharyngoplasty, involves removal of a portion of the soft palate to prevent closure of the pharyngeal airway during sleep. However, this operation is not always effective and may result in undesirable complications, such as nasal regurgitation.
A wide variety of non-surgical approaches for treating sleep disorders have also been proposed including the use of oral cavity appliances. It has been previously recognized that movement of the mandible (lower jaw) forward relative to the maxilla (upper jaw) can eliminate or reduce sleep apnea and snoring symptoms by causing the pharyngeal air passage to remain open. Several intra-oral dental appliances have been developed which the user wears at night to fix the mandible in an anterior, protruded (i.e. forward) position. Such dental appliances essentially consist of acrylic or elastomeric bite blocks, similar to orthodontic retainers or athletic mouth guards, which are custom-fitted to the user's upper and lower teeth and which may be adjusted to vary the degree of anterior protrusion.
U.S. Pat. No. 4,901,737, which issued to Toone on 20 Feb., 1990, exemplifies the prior art. Toone discloses an intra-oral appliance for reducing snoring which repositions the mandible in an inferior (open) and anterior (protrusive) position as compared to the normally closed position of the jaw. Once the dentist or physician determines the operative “snore reduction position” for a particular patient, an appropriate mold is taken of the maxillary dentition and of the mandibular dentition for formation of the appliance template. The Toone appliance includes a pair of V-shaped spacer members formed from dental acrylic which extend between the maxillary and mandibular dentition to form a unitary mouthpiece. In an alternative embodiment of the Toone invention, the spacer members are formed in two pieces and a threaded rod is provided to enable adjustment of the degree of mandibular protrusion or retrusion after the mouthpiece is formed.
European patent application No. 0,312,368 published Apr. 19, 1989 also discloses an intra-oral device for preventing snoring. This device consists of a U-shaped mouthpiece which conforms to the upper dental arch of the user and includes a sloped, lower ramp for engaging the mandibular dentition. Normal mouth motions, such as the clenching of the jaw, will cause some of the mandibular dentition to engage the underside of the ramp, thereby camming the lower jaw forward to increase the spacing between the base of the tongue and the posterior wall of the pharynx.
While prior art dental appliances have proven effective in maintaining the mandible in a protruded position to improve airway patency, they often result in undesirable side effects. One of the most common side effects is aggravation of the tempromandibular joint and related jaw muscles and ligaments, especially in individuals who have a tendency to grind their teeth during sleep. Aggravation of the tempromandibular joint has been associated with a wide variety of physical aliments, including migraine headaches. Accordingly, many individuals suffering from sleep apnea and snoring disorders are not able to tolerate existing anti-snoring dental appliances for long periods of time.
Recently it has been suggested that nocturnal teeth grinding or “bruxism” is also closely associated with partial occlusion of the pharyngeal airway during sleep. One hypothesis is that bruxism is in fact a reflex action employed by mammals to help maintain the patency of their airways. It appears that the physical clenching of the jaw which occurs during bruxism can function as an anatomical splint preventing or lessening airway occlusion. However, bruxism has several deleterious side effects, most notably gradual wear of the dental enamel. Many consumers wear mouth guards to prevent enamel wear, but such guards do not prevent or mitigate the underlying sleep disorder.
As mentioned above, the bruxing reflex can also cause problems in patients using intra-oral dental appliance configured for treatment of snoring and sleep apnea. Sleep studies suggest that bruxing individuals have a tendency to habitually move their jaws in a generally elliptical motion. This motion can cause threaded connectors coupling upper and lower dental bite blocks together to gradually loosen and eventually shear. Replacement of fractured connecting pins is inconvenient to consumers and potentially expensive to warranty providers.
The applicant's prior dental appliances for treatment of snoring and sleep apnea are designed to maintain the mandible in a preferred anterior position while also allowing a limited degree of lateral excursion of the mandible relative to the upper jaw to avoid discomfort to the tempromandibular joint and related muscles and ligaments. The applicant has also recently determined that it may also be beneficial in some patients, such as patients prone to nocturnal bruxism, to allow for a significant degree of anterior (i.e forward) excursion of mandible relative to the upper jaw in the protruded position. This allowance for anterior excursion permits habitual elliptical movement of the jaw while anatomically maintaining the patency of the pharyngeal airway. The combined effect appears to be a substantial reduction in bruxing muscular activity during sleep. Moreover, it appears that, if anterior excursion of the mandible is permitted in the protruded position, less anterior advancement of the mandible relative to the upper jaw may be necessary to achieve a reduction in snoring and apneic episodes. This in turn can reduce side effects associated with long-term wear of anti-snoring dental appliances, such as bite displacement and misalignment.